1. Field of the Invention
This invention lies in the field of manufactured articles comprised of fiber reinforced engineering resin laminated composites, and includes apparatus and methods for making such articles from preformed prepregs.
2. Prior Art
In the art of composites, it is common to prepare prepregs of so-called engineering resins and reinforcing fibers. From the prepregs, composites (including laminated composites) are prepared.
To fabricate composites from prepregs, various forming techniques can be used, such as a so-called stamp molding procedure or the like, the techniques typically employing elevated temperatures and pressures. The art of fabricating composites from prepregs is relatively young and is characterized by unsolved fabrication problems. A problem has existed, for example, in forming three-dimensional, integral one-piece composite structures which are comprised of two different types of starting prepregs, a first type being identified herein as a first prepreg type which comprises a resin layer generally uniformly impregnated with an arrangement of substantially continuously extending ordered fibers, in a form such as a woven fabric, or a unidirectionally arranged array of spaced, parallel continuous fibers, and a second type being identified herein as a second prepreg type which comprises a resin layer generally uniformly impregnated with substantially randomly arranged reinforcing fibers, in a form such as a fiber mat, or randomly dispersed chopped fibers. The first such type of prepreg is well suited for use in the manufacture of flattened components to be used as wall portions or other similar flattened members, while the second such type of prepreg is well suited for use in the manufacture of three dimensional components to be used as frame or supporting portions or other similar projecting members. Such three-dimensional components preferably have a base portion that is securable to such a wall portion and also one or more integrally formed raised or projecting and upstanding portions, such as rib, frame, and support members, brackets, flanges, projections, platforms, and the like.
The principle reason for the differences in suitability between these respective first and second prepreg types arises out of the circumstance that the first such type of prepreg is difficult to mold into three dimensional members incorporating a major raised projection because ordered continuous reinforcing fibers in a prepreg are found to be difficult to stretch or elongate to an extent such as may be necessary to produce a product composite having undamaged fiber reinforcement in a projecting portion (depending, of course, somewhat upon the location and height of the raised portion relative to the adjacent surrounding base regions). However, in a prepreg, such as one of the second type containing a randomly arranged mat of fibers, there is a demonstrated capacity under the application of heat and pressure for both resin and reinforcing fiber to move transversely in a base region and outwardly away from the base region along with the impregnating resin, thereby permitting production of a product composite having a desired three dimensional structure which is substantially fully fiber reinforced.
A two-step composite manufacturing procedure, where, for example, a composite wall component is fabricated in one operation or step, and composite frame components (for supporting and rigidifying the wall component) are fabricated in another operation or step, and then the resulting respective components are somehow adhesively bonded or mechanically fastened together, is generally objectionable. For one thing, it is difficult to get a close fit between two such separately fabricated different composite components. Because of the rigidity and strength characteristically associated with composite components at ambient temperatures and pressures, fits and fit adjustments are difficult to achieve. For another thing, the surface characteristics of fabricated composite components make it difficult to adhesively bond such together using, for example, an adhesive substance which is applied between interfacially contacted component surfaces in a separate step after component fabrication. For another thing, the toughness of the respective separately fabricated components makes it difficult, and also time and labor consuming, to fasten such securely together by mechanical means, such as by rivets, nut and bolt assemblies, or the like.
The art of composite manufacture needs an improved technique for making integrated composite structures incorporating both above-indicated first and second types of fiber reinforced prepreg structures wherein each type is used to make respective component portions for which it is best suited.